The flaring or assisted open combustion of undesired process by-product streams is commonly used to oxidize and convert toxic gases and vapors to their less harmful combustion products for release into the environment. A mixture of the undesired product and a fuel are directed to the base of the flare stack to form a feedstream that rises to the flare tip or stack outlet where the mixture is ignited in the combustion zone to form the flare or flame. The efficient and complete combustion of the mixture is not always achieved. When the process is not properly managed, smoke is also produced by this process. Smoke can be an indicator that the combustion process is incomplete, and that the toxic or otherwise undesired process materials have not been converted to less harmful forms. Smoke is also a visible constituent of air pollution, and its elimination or reduction is a consistent operational goal.
In order to reduce smoke production, the installation of air and steam systems in conjunction with flaring stacks has been undertaken by the prior art. The low-pressure air assist system uses forced air to provide the air and fuel mixing required for smokeless operation. A fan, commonly installed in the bottom of the flare stack, provides the combustion air required. Steam assisted flare systems use a steam ring and nozzles to inject steam into the combustion zone at the flare tip where air, steam and fuel gas are mixed together to produce a smokeless flame. In some systems of the prior art, a concentric banner or shield is provided that surrounds the flare tip or outlet.
Steam and low-pressure air assists for flaring are in common use because both systems are considered by the art to be generally effective and relatively economical as compared to alternative means for disposing of the undesired by-products.
However, both of these prior art systems have various drawbacks and deficiencies. The low-pressure air assists requires a significant capital expenditure for at least one fan that must be dedicated to the flare stack. Continuous operation imposed a rigorous maintenance schedule and even a back-up system in case of a breakdown or major repairs.
Steam assist systems can require sophisticated control devices, have relatively high utility requirements and maintenance/replacement schedules.
Various methods and configurations of apparatus have been proposed in the disclosures of the patent literature to improve the efficiency of combustion of flare stacks. For example, U.S. Pat. No. 5,788,477 discloses a ring manifold fitted with an array of nozzles that can be directed inwardly, upwardly and at an angle that is displaced laterally to inject high pressure air jets above the outlet of the fuel gas at the tip of the stack. Similarly, in U.S. Pat. No. 4,652,232, a plurality of nozzles are mounted on a high pressure fluid manifold that encircles the stack and emits the fluid at or somewhat above the level of the rim of the waste gas stack, and the nozzles are angled upwardly.
Other constructions are disclosed and discussed in U.S. Pat. No. 4,019,852 as the background in the art.
In the constructions of the first two prior art patents, the nozzles or manifolds containing the high pressure fluid outlets are in close proximity to the flame, if not engulfed by the flame under foreseeable atmospheric conditions crosswinds. The maintenance and replacement costs associated with these arrangements can be significant.
It is therefore a principal object of the present invention to provide an apparatus and method for enhancing the complete combustion of flare gases that is less expensive to install, requires minimal maintenance, and is adaptable to the varying operating conditions found in industrial plant operations.
Another object of the invention is to provide a method and apparatus that is readily adapted for use with existing flare stacks without significantly modifying the existing stack tip or outlet configurations.